June, Are you a geneticist? As a geneticist I would say highly unlikely, but not impossible. Every once in a while there are new mutations that pop up, it's why we have so much variety in the species to begin with. It's usually highly rare, so I would agree with your suspicions, however if they say that they have no black chickens, there are 2 other explanations: someone else's hen laid the egg or rooster fertilized it (non-paternity/maternity) or the chick has a new mutation (rare, but not impossible).Have you, at any point in the last 3 months, had a different rooster or cockerel? The black chicks are not possible with the stated parents. The black pattern gene is the most dominant of all pattern genes. It does not hide. It simply is not possible. Neither of your claimed parents are black. They can not produce a black chick. They do not have the genes required to produce such chicks.